sql: cast string to int[] or decimal[] when appropriate

[rafiss]

The following works in postgres, but not CockroachDB.

> create table arrtest (intarr int[], decarr decimal(2,1)[], strarr text[]);
CREATE TABLE

> INSERT INTO arrtest VALUES ('{1,2,3}','{3.1,1.4}', '{abc,f''a,"fa\"b",def}');
pq: value type string doesn't match type int[] of column "intarr"

Adding explicit casts makes it work.

> INSERT INTO arrtest VALUES ('{1,2,3}'::int[],'{3.1,1.4}'::decimal[], '{abc,f''a,"fa\"b",def}');
INSERT 1

[jordanlewis]

This should work via our constant upcast mechanism, which currently only automatically upcasts strings into string arrays. This should be a relatively straightforward addition.

See pkg/sql/sem/tree/constant.go, and notice how only StringArray is present in StrValAvailAllParsable.